GPS Measurement of Philippine Sea Plate Motion in the Nansei-Shotou Region

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The Philippine Sea plate is subducting beneath the Eurasian plate along the Ryukyu trench in the Nansei-shotou region, southwest Japan. We have so far carried out three times GPS campaign at three island stations in the Nansei-shotou GPS network extending across the Ryukyu trench. Analyzing GPS data observed with dual frequency GPS receivers WM102, we detected the relative motion of these two plates. From the change of 3 baseline lengths during about 2 years from January 1990 to November 1991, the Philippine Sea plate is estimated to move toward the Eurasian plate with a convergence rate of 8.7 <plus-minus> 3.1 cm/yr and a direction of N70ﾟ <plus-minus> 30This study shows that GPS observations can directly detect plate motions. Further, we need to construct a fixed GPS network and perform daily or weekly GPS observations for detecting the details of plate motion, that is, iregular or stationary motion.